Positions for both celestial and terrestrial objects are specified in spherical coordinates. Celestial navigation becomes complicated by the fact that these spherical coordinates must be converted to rectangular coordinates for representation and positional location on flat charts or maps. Accordingly, current procedures for celestial navigation generally require cumbersome and highly sophisticated equipment, as well as volumes of resource materials and considerable navigational training for proper use. Some of the equipment requires use of an assumed position, or that only certain selected reference stars such as the North Star, Polaris, be used. When that star is not visible, such equipment cannot be employed. Typically, plotting boards, maps or charts, and volumes of tables as well as a knowledge of spherical trigonometry or of the navigational triangle are required to be employed along with the currently commonly used navigational devices such as the sextant or transit. Simple "special cases" exist, such as the meridian crossings of celestial objects. These have the disadvantage that they require several sightings over an extended period of time, and can rarely be used for twilight sightings.
While the space requirements for navigational instruments and supplementary materials may not be objectionable on board large ships, they may become so where space is at a premium such as on smaller vessels, in aircraft or during land exploration. While modern computers afford an avenue for memory storage of tables, and the algorithms for the computations, they are not reliable in case of emergency for most uses, such as land exploration or small vessels. In addition, these instruments are highly complex, delicate, and may require power sources which are not available. In addition, highly sophisticated electronic equipment is highly subject to corrosion and malfunction under adverse exploration or nautical conditions.
Efforts to develop mechanical equipment which requires less space and which may be easier to use for a person without extensive navigational training have met with only limited success. For example, the Storer U.S. Pat. No. 2,316,466 and the Cable U.S. Pat. No. 2,566,312 both are dependent for their operation on the visibility of the pole star.
The Cable instrument is discussed in Herrick, S., "Instrumental Solution in Celestial Navigation," Navigation, Vol. 1, No. 2, June 1946, pages 22-27. In addition, FIG. 4 thereof shows and instrument for determination of latitude and longitude from simultaneous observation of two stars. The Herrick instrument design is illustrated as mounted on a yoke with a gyro-stabilized base. Herrick uses a pair of sidereal hour angle circles which are separated by the yoke mount into which a sighting tube is journaled. It is not clear that this instrument was in fact built as it is stated therein to be conceived of as a part of a more elaborate mechanism involving gyrostabilization, clockwork and a compass repeater.
Other references illustrative of the art are Maloney, Elbert S., Dutton's Navigation and Piloting, Naval Institute Press, Annapolis, MD., 1978; Bowditch, Nathaniel, American Practical Navigator, Defense Mapping Agency Hydrographic Center, Washington, D.C. 20390, 1977; Saegmuller, U.S. Pat. No. 914,954; Kittelson, U.S. Pat. No. 2,527,189; Pierce U.S. Pat. No. 3,046,830; MacDonald, U.S. Pat. No. 3,207,025; and Owen, U.S. Pat. No. 4,083,636; Zeiss Ikon, German Pat. No. 474,100, Mar. 14, 1929; and Hopp, British Pat. No. 960,383, published Jun. 10, 1964.
Accordingly, there is a need for a mechanical/optical instrument of relatively compact size which is especially suited to use in small boats, lifeboats or expeditions where space, equipment and expertise may be limited. The present invention provides such an instrument which requires for supplementary material only the very minimum: a watch, a current Nautical Almanac (such as Nautical Almanac for the year 1980 obtainable from the U.S. Government Printing Office, Washington, D.C. 20402) and simple writing materials. The present instrument does not require knowledge of spherical trigonometry or of the navigational triangle. No complex sight reduction tables, plotting boards or even charts are needed. Sight reductions can be carried out by use of simple arithmetic.
In the principal embodiment the instrument of the present embodiment is completely optical/mechanical in its construction and has no batteries to run down or corrode. No assumed position is needed for sight reduction so that faulty information, or lack of information concerning one's position is not a disadvantage. The horizon portion of the instrument of the present invention may be aimed at either the east or west horizon in use allowing the user to use one horizon if the other is obscured or obstructed from view. The instrument is also natural for its human user in that the user can pick a star and directly sight a telescope/periscope element at the star. The user faces directly toward the celestial object being used, and thus finding and holding a star in the instrument's field of view is both natural and easy. The instrument can also be equipped with a bubble horizon or other artificial horizon for use in the air or on land where the natural horizon may not be usable. In another embodiment a simple gearing mechanism may permit tracking stars automatically.